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International Harvester’s Torque Amplifier in 1954 Sparked a Revolution

International Harvester Company’s (IHC) introduction of a torque amplifier now seems like a minor improvement in light of the advanced full powershift transmissions offered on today’s high-horsepower tractors. When IHC’s torque amplifier (TA) came out in 1954, it marked a revolution in transmission engineering. For the first time, farmers could shift a tractor between two gears, not only on-the-go but also under load – without having to use the clutch or throttle the engine down.

boost draft on demand

The advantages of this maneuver were huge, particularly when tilling. The TA gave farmers the ability to shift a tractor down, thereby, generating more draft – an invaluable aid when encountering a tough spot in the field.

So popular was this feature that within the decade, the TA was available on most high-horsepower tractors.

This IHC exclusive design was located in the tractor’s clutch housing. The device consisted of a planetary drive operating off its own manually operated, single-disk clutch that drove the input shaft of the regular five-speed transmission.

When the TA’s clutch was engaged, the planetary drive was locked up to deliver a 1-to-1 gear ratio to the transmission. 

When the tractor was shifted from direct drive to torque amplification, the clutch would release and the travel speed of the tractor was reduced about 32%. This increased pulling ability by almost 48%, due to a gear ratio increase of 1.482-to-1.

The beauty of IHC’s TA was that the number of available gears doubled to 10 in a standard five-speed transmission. Plus, the TA could be engaged and disengaged without using the tractor’s clutch or regulating engine speed.

first power-shift tranny

In some ways, the IHC design could be called the first power-shift transmission, since it allowed shifting between gear sets while under power. IHC originally offered the TA on its Farmall Super M-TA, Super MD-TA (diesel), and the McCormick Super W6-TA. This planetary-type TA was to remain in production on some IHC tractors of less than 70 hp. until 1980.

The Super M-TA is also notable for being the first IHC tractor to come equipped with an independent or live PTO, which continued to work even after the transmission was disengaged.

other international harvester firsts

  • 1919: First commercial application of a PTO on a tractor. A year later, the PTO would become standard equipment on the model 15-30.
  • 1924: First row-crop tractor, with the introduction of the McCormick-Deering Farmall Regular.
  • 1929: First tractor-mounted corn picker.
  • 1942: First commercially produced spindle-type cotton picker.
  • 1952: First fast-hitch system for tractors, with the introduction of the Farmall Fast-Hitch.
  • 1961: First tractor equipped with a hydrostatic transmission, with the introduction of the HT-340 turbine tractor in Britain. IHC would go on to introduce the first combine and cotton picker (in 1965) and garden tractor (1967) equipped with a hydrostatic drive.
  • 1977: First rotary-type combine, with the introduction of the IHC Axial-Flow combine.
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